Method and apparatus for discontinuous reception of connected terminal in a mobile communication system

ABSTRACT

A method and apparatus for controlling an active time period during a Discontinuous Reception (DRX) operation in a User Equipment (UE) in a mobile communication system. The method includes transitioning to an active state from a sleep state; extending an active time of the active state, if control data indicating transmission of new user data is received on a control channel; receiving a control signal indicating a termination of the active time; and transitioning to the sleep state from the active state, based on the control signal.

PRIORITY

This application is a Continuation of U.S. application Ser. No.13/909,605, which was filed in the U.S. Patent and Trademark Office onJun. 4, 2013, which is a Continuation of U.S. application Ser. No.13/608,590, which was filed in the U.S. Patent and Trademark Office onSep. 10, 2012 and issued as U.S. Pat. No. 8,457,588 on Jun. 4, 2013,which is a Continuation of U.S. application Ser. No. 11/729,032, whichwas filed in the U.S. Patent and Trademark Office on Mar. 28, 2007 andissued as U.S. Pat. No. 8,270,932 on Sep. 18, 2012, and claims priorityunder 35 U.S.C. §119(a) to Korean Patent Applications filed in theKorean Intellectual Property Office on Mar. 28, 2006 and on Sep. 6,2006, which were assigned Serial Nos. 10-2006-0027986 and10-2006-0085757, respectively, the entire disclosure of each of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a Discontinuous Reception(DRX) operation in a mobile communication system. More particularly, thepresent invention relates to a method and apparatus for performing a DRXoperation using a variable active period in a connected terminal.

2. Description of the Related Art

The wireless communication system was in large measure designed becausea communication device has no access to the fixed wired network. Suchwireless communication systems include mobile communication systems,Wireless Local Area Network (WLAN), Wireless Broadband (WiBro), andmobile ad hoc systems.

In particular, mobile communication systems are based on user mobility,compared to other wireless communication systems. They ultimately aim toprovide communication services to mobile terminals such as portablephone and wireless pagers irrespective of time and location.

Mobile communication systems operate synchronously or asynchronously.Particularly, Universal Mobile Telecommunication Service (UMTS) is a3^(rd) Generation (3G) asynchronous mobile communication systemoperating in Wideband Code Division Multiple Access (WCDMA), based onthe European mobile communication systems, Global System for MobileCommunications (GSM) and General Packet Radio Services (GPRS). The3^(rd) Generation Partnership Project (3GPP) working on UMSTstandardization is now discussing the future-generation UMTS systemcalled Long Term Evolution (LTE).

LTE is a technology for high-speed packet communications at or above 100Mbps, seeking commercialization around 2010. To do so, many schemes areunder study, for example, a method for reducing the number of nodesexisting on a communication path by simplifying the networkconfiguration or the method for approximating wireless protocols toradio channels as close as possible. Eventually, the LTE system will bechanged from the existing 4-node architecture to a 2-node or 3-nodearchitecture.

FIG. 1 illustrates the configuration of an LTE system to which thepresent invention applies.

Referring to FIG. 1, the LTE system can be simplified to a 2-nodearchitecture with Evolved Node Bs (ENBs) 100 a to 100 e and EvolvedGateway GPRS Serving Nodes (EGGSNs) 102 a and 102 b.

ENBs 100 a to 100 e, which are equivalent to existing Node Bs, areconnected to a User Equipment (UE) 104 by a radio channel. Compared tothe conventional Node Bs, ENBs 100 a to 100 e provide more complexfunctionalities.

This implies that all user traffics including real-time service such asVoice over Internet Protocol (VoIP) are serviced on shared channels andthus a device for collecting status information of the particular UE 104and other UEs and scheduling them is required in the LTE system. ENBs100 a to 100 e are responsible for the scheduling.

To achieve data rates of up to 100 Mbps, the LTE system is expected touse a wireless access technology called Orthogonal Frequency DivisionMultiplexing (OFDM) in a 20-MHz bandwidth. Adaptive Modulation andCoding (AMC) will be applied to UE 104 according to its channel status.That is, a modulation scheme and a channel coding rate are adaptivelyselected for UE 104 according to the channel status.

Like High Speed Downlink Access (HSDPA) or Enhanced uplink DedicatedChannel (E-DCH), the LTE system will use Hybrid Automatic Repeat reQuest(HARQ) between UE 104 and ENBs 100 a to 100 e. HARQ is a scheme forincreasing the reception success rate by soft-combining initialtransmission data with retransmission data without deleting the formerdata. Thus, UE 104 intends to ensure the reception performance ofpackets by the AMC and HARQ schemes.

Conventionally, a UE wakes up at a predetermined time, monitors apredetermined channel for a predetermined time period, and then entersagain into a sleep mode in an idle state. This is called DiscontinuousReception Operation (DRX), which is a way to lengthening the waitingtime of the idle-state UE.

FIG. 2 illustrates the timing of DRX operation in a conventional mobilecommunication system.

Referring to FIG. 2, a UE and a Node B agree on a DRX configuration, thesleep period and an alternate active period according to the DRXconfiguration. The sleep period is a time period during which the UEturns off its receiver, thus minimizing power consumption. The activeperiod is a time period during which the UE performs a normal receptionoperation with its receiver turned on. The active period is also calleda wake-up period and thus the terms “active period” and “wake-up period”are interchangeably used in the same meaning herein.

The DRX configuration is typically composed of the following elements.

1. DRX cycle length 210 or 220: the interval between an active periodand the next active period. With the DRX cycle length, the sleep mode isincreased, and the power consumption of the UE is decreased. Yet, theincreased DRX cycle length increases the paging delay in the UE. Anetwork signals the DRX cycle length.

2. Starting position of an active period 205, 215 or 225: The startingposition of an active period is derived from the Identifier (ID) of theUE and the DRX cycle length. For example, the starting position of theactive period is calculated by modulo operation of the UE ID and the DRXcycle length.

3. Active period length 235: a timer period during which the UE is keptawake in one active period. Typically, the active period length ispreset. For example, the active period length is 10 msec in the UMTScommunication system.

The UE calculates the starting position 230 of an active period usingthe UE ID and the DRX cycle length 210 or 220 and receives a downlinkchannel for the active period counted from the starting position 230. Inthe absence of desired information on the downlink channel, the UE turnsoff its receiver and enters into a sleep period.

The classic DRX operation of waking up at every predetermined timeinterval and monitoring the downlink channel for a predetermined timeperiod illustrated in FIG. 2 is not feasible for a connected UE in thenovel LTE system.

When the UE is connected, it means that a particular service is inprogress for the UE and user data associated with the service existsbetween the network and the UE. The network, capable of Radio LinkControl (RRL), preserves the service context for the UE. The UE in thisstate is called a connected UE.

Accordingly, there exists a need for specifying a DRX operation of aconnected UE in the LTE system, in relation to the conventional DRXoperation of an idle-state UE.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed below.

Accordingly, an aspect of the present invention is to provide a methodand apparatus for a connected UE in a mobile communication system toperform a DRX operation.

Another aspect of the present invention provides a method and apparatusfor setting a DRX cycle variable, taking into account the amount ofpacket data in a UE in a future-generation mobile communication system.

A further aspect of the present invention provides a method andapparatus for adjusting the active period length for a UE.

In accordance with an aspect of the present invention, a method forwireless communication is provided, which includes transitioning to anactive state from a sleep state; extending an active time of the activestate, if control data indicating transmission of new user data isreceived on a control channel; receiving a control signal indicating atermination of the active time; and transitioning to the sleep statefrom the active state, based on the control signal.

In accordance with another aspect of the present invention, an apparatusfor wireless communication is provided, which includes a receiver; and acontroller configured to transition the apparatus to an active statefrom a sleep state, extend an active time of the active state, ifcontrol data indicating transmission of new user data is received on acontrol channel through the receiver, receive, through the receiver, acontrol signal indicating a termination of the active time, andtransition the apparatus to the sleep state from the active state, basedon the control signal.

In accordance with another aspect of the present invention, a method forwireless communication is provided. The method includes transmitting, bya Node B, information for deriving a starting position of an activestate to a user equipment (UE); transmitting, by the Node B, to the UE,control data on a control channel, the control data indicatingtransmission of new user data; and transmitting, by the Node B, acontrol signal indicating a termination of an active time. The activetime of the active state is extended, if the control data indicating thetransmission of the new user data is transmitted.

In accordance with another aspect of the present invention, an apparatusfor wireless communication is provided, which includes a transmitter;and a controller configured to transmit, to a user equipment (UE),through the transmitter, information for deriving a starting position ofan active state, transmit, to the UE, through the transmitter, controldata on a control channel, the control data indicating transmission ofnew user data, and transmit, through the transmitter, a control signalindicating a termination of an active time. The active time of theactive state is extended, if the control data indicating thetransmission of the new user data is transmitted.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present invention will be more apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates the configuration of an LTE system to which thepresent invention applies;

FIG. 2 illustrates the timing of DRX operation in a conventional mobilecommunication system;

FIG. 3 illustrates a DRX operation with a variable active period lengthaccording to the present invention;

FIG. 4 is a flowchart of an operation of a UE in case of in-bandsignaling of the end of an active period according to the presentinvention;

FIG. 5 is a flowchart of an operation of the UE in case of out-bandsignaling of the end of an active period according to the presentinvention;

FIG. 6 is a flowchart of an operation of the UE when the MS determinesthe end of an active period, taking into account downlink activityaccording to the present invention;

FIG. 7 is a block diagram of a UE receiver according to the presentinvention;

FIG. 8 illustrates the timing of DRX operation considering an RLCACKnowledgement (ACK) signal according to the present invention;

FIG. 9 is a flowchart of the DRX operation considering an RLC ACK signalin the UE according to the present invention; and

FIG. 10 is a block diagram of a UE receiver according to the presentinvention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The matters defined in the description such as detailed construction andelements are provided to assist in a comprehensive understanding of theinvention. Accordingly, those of ordinary skill in the art willrecognize that various changes and modifications of the embodimentsdescribed herein can be made without departing from the scope and spiritof the invention. Also, descriptions of well-known functions andconstructions are omitted for clarity and conciseness.

While exemplary embodiments of the present invention are described inthe context of an LTE system, it is to be understood that they areapplicable to other mobile communication systems using DRX withoutmodification.

The exemplary embodiments of the present invention define a DRXoperation for a connected UE in a future-generation mobile communicationsystem. Preferably but not necessarily, the DRX of the connected UE isconfigured, taking into account service characteristics. A differentamount of data may be generated for the connected UE every DRX cycledepending on service type. In other words, the duration for which the UEmonitors the downlink channel needs to be changed in each DRX cycleaccording to the amount of data to be sent during the DRX cycle.

For example, when the UE receives a file download service usingTransmission Control Protocol (TCP), in view of the nature of TCP, onepacket is initially sent on the downlink, two packets are sent inresponse to a TCP ACK from the UE, and then four packets are sent inresponse to the TCP ACK for the two packets from the UE. The TCP filedownload service is characterized in that downlink data increases with acertain time spacing between transmissions. Considering this tendency,it is preferable to gradually increase the length of an active periodfor the UE in the service.

Besides the file download service, unpredictability and discontinuity indata generation are characteristics of packet services. Thus, a packetservice may face different traffic generation status in every DRX cycle.Accordingly, the exemplary embodiments of the present invention areintended to provide a method for setting a DRX cycle that variesaccording to the amount of packet data in the UE.

Referring to FIG. 3, a Node B signals a DRX cycle length 310,information for deriving the starting position 305 of an active period350 (hereinafter, referred to as starting position derivinginformation), and a minimum active period length 340 a or 340 b.

The UE wakes up at each of the starting positions 305, 320 and 325 ofactive periods 350, 360 and 370. In the absence of data to receive, theUE is kept for the minimum active period length and enters into a sleepmode. In the presence of data to receive, the UE maintains the activeperiod until receiving the data completely and then enters into thesleep mode.

The UE calculates the starting position 305 of the active period 350 ina predetermined method, for example, by modulo operation of the ID ofthe UE and the DRX cycle length. When the active period starts at time305, the UE is activated.

The lengths of active periods 350, 360 and 370 range from the minimumlength 340 a or 340 b to the DRX cycle length 310 or 380. At thestarting position 305 of the active period 350, the UE receives a packeton a downlink channel. Reference numerals 340 a and 340 b denoteidentical minimum active period length.

As to the active period 360, packets are successively received for theminimum active period length 340 a. The UE can terminate the activeperiod 360 by determining if each received packet is the last one in apredetermined method.

The packet reception can be carried out in a predetermined methoddepending on the communication system. For example, in the LTE system,the UE monitors the downlink control channel to determine where there isa packet to receive and in the presence of a packet to receive, itreceives the packet.

As to the active period 370, the UE wakes up at time 325 and finds outthat there is no packet to receive during the predetermined minimumactive period length 340 b. Thus, the UE terminates the active period370 and transitions to the sleep mode until the next active periodcomes.

On the other hand, when the UE wakes up at time 320 and determines thepresence of a packet to receive before the minimum active period length360 expires, it starts to receive packets from the Node B.

The end positions of active periods 350, 360 and 370 are signaled byin-band information included in a packet or by a control channel. Or theUE can autonomously determine the end positions of active periods 350,360 and 370 in accordance with a predetermined rule.

1. In the case where the end of an active period is notified by in-bandinformation, the Node B sets a 1-bit Last Packet Flag to YES in the lastpacket during the active period. Upon receipt of the packet with theLast Packet Flag set to YES, the UE maintains the active period untilpackets stored in an HARQ processor at the time when the UE detects thatthe packet is the last one are completely processed and when theprocessing is completed, the UE enters into the sleep mode.

2. When the end of an active period is notified by a control channel,the UE maintains the active period until packets under processing in theHARQ processor at the time when the termination of the active period isdeclared are received and when the reception is completed, the UEtransitions to the sleep mode.

3. If no packets are received for a predetermined time period, the UEcan transition to the sleep mode, considering that the active period hasbeen terminated.

As described above, in the absence of any packet to receive, the activeperiod is kept for the minimum active period length. In the presence ofany packet to receive, the end of the active period is signaled byin-band information or an out-band signal in the control channel, or theend of the active period is determined autonomously by the UE. In thisway, the active period is adjusted to a variable length, when needed,thereby ensuring an efficient DRX operation.

Embodiment 1

Referring to FIG. 4, when the end of an active period is notified by theLast Packet Flag, the UE operates in the following way.

The UE receives information about a DRX cycle length, starting positionderiving information, and a minimum active period length during a callsetup in step 405. Then the UE prepares for a DRX operation.

In step 410, the UE derives the starting position of an active periodfrom the starting position retrieved information, for example, an ID ofthe UE and the DRX cycle length and determines if the starting positionof the active period has come.

If the active period has not started yet, the UE is kept in the sleepperiod until the starting position of the active period in step 435. TheUE is aware that the active period starts the DRX cycle length after thestarting position of the previous active period.

When the active period starts, the UE activates a timerT(DRX_CYCLE_LENGTH) and a timer T(MINIMUM_ACTIVE) in step 415. The timerT(DRX_CYCLE_LENGTH) is a timer set to the DRX cycle lengthT(DRX_CYCLE_LENGTH) and the timer T(MINIMUM_ACTIVE) is a timer set tothe minimum active period length T(MINIMUM_ACTIVE).

In step 420, the UE monitors the shared control channel to determine ifthere is a packet to receive. If no packets to receive exist until thetimer T(MINIMUM_ACTIVE) expires, the UE is placed in the sleep modeuntil the next active period starts in step 435. The next active periodstarts when the timer T(DRX_CYCLE_LENGTH) expires.

Conversely, if there is any packet to receive before the timerT(MINIMUM_ACTIVE) expires in step 420, the UE receives the packetaccording to an HARQ operation in step 425. If the packet issuccessfully received, the UE checks the Last Packet Flag of thereceived packet in step 430.

If the Last Packet Flag is set to YES, the UE goes to step 440. If theLast Packet Flag is set to NO, the UE returns to step 425 to continuethe packet reception.

In step 440, the UE completes processing of HARQ packets stored in theHARQ processor when it finds out that the received packet is the lastone. Then the UE enters into the sleep mode until the next active periodstarts. The next active period starts when the timer T(DRX_CYCLE_LENGTH)expires.

The completion of processing of HARQ packets means that a packet storedin the HARQ processor is normally received by the HARQ operation andthus an HARQ ACK is sent for the packet, or despite errors in thepacket, a new packet is received in the same HARQ process and thus thereception of the packet is eventually failed in the HARQ operation.

That is, when a packet stored in the HARQ processor is successfullyreceived or the UE determines that the successful reception of thepacket is not possible, it is said that the packet is completelyprocessed.

Embodiment 2

Referring to FIG. 5, the UE operates in the same manner as in the firstexemplary embodiment of the present invention, except for the way the UEdetermines the termination of an active period. Hence, the followingdescription is made on different steps from those illustrated in FIG. 4.That is, steps 505 to 520 of FIG. 5 will not be described since they areperformed in the same manner as steps 405 to 420 of FIG. 4.

In step 525, the UE receives a packet from the Node B according to apredetermined HARQ protocol.

As the UE continues receiving the downlink control channel, it monitorsreception of a signal indicating the end of the active period on thedownlink control channel in step 530.

Upon receipt of the signal, the UE proceeds to step 540 and otherwise,the UE returns to step 525 to continue the packet reception.

The UE completes processing of the HARQ packets, which exist in the HARQprocessor at the time when it receives the signal indicating the end ofthe active period in step 540 and enters into the sleep mode until thenext active period starts in step 535. The next active period startswhen the timer T(DRX_CYCLE_LENGTH) activated in step 515 expires.

Embodiment 3

Referring to FIG. 6, the UE receives information about a DRX cyclelength, starting position deriving information, a minimum active periodlength, and an active period end interval during a call setup in step605. Then the UE prepares for a DRX operation. The minimum active periodlength may be equal to the end of the active period interval. In thiscase, only one of both can be signaled. Then the UE prepares for a DRXoperation.

In step 610, the UE derives the starting position of an active periodfrom the starting position retrieved information, for example, an ID ofthe UE and the DRX cycle length and determines whether the startingposition of the active period has come.

If the active period has not started yet, the UE is kept in the sleepperiod until the starting position of the active period in step 635. Thestart position of the active period is derived from the startingposition retrieved information, and the next active period starts theDRX cycle length after the starting position of the previous activeperiod.

When the active period starts, the UE activates a timerT(DRX_CYCLE_LENGTH) and another timer T(MINIMUM_ACTIVE) in step 615.Timer T(DRX_CYCLE_LENGTH) is a timer set to the DRX cycle lengthT(DRX_CYCLE_LENGTH) and timer T(MINIMUM_ACTIVE) is a timer set to theminimum active period length T(MINIMUM_ACTIVE).

In step 620, the UE monitors a shared control channel to determine ifthere is a packet to receive. If no packets to receive exist until thetimer T(MINIMUM_ACTIVE) expires, the UE is placed in the sleep modeuntil the next active period starts in step 635. The next active periodstarts when the timer T(DRX_CYCLE_LENGTH) expires.

Conversely, if there is any packet to receive before the timerT(MINIMUM_ACTIVE) expires in step 620, the UE receives the packetaccording to the HARQ protocol in step 625.

In step 627, the UE starts (or restarts) a timer T(active_period_end)set to the active period end interval T(active_period_end). The timerT(active_period_end) is used to terminate the active period, unless apacket is received for the time T(active_period_end). The UE starts thetimer T(active_period_end) upon receipt of the initial packet andrestarts it each time the UE receives a following packet.

The following packet can be (1) a new packet or (2) either of a newpacket or a retransmission packet.

That is, the UE can restart the timer T(active_period_end) only when thefollowing packet is a new packet, or when the following packet is eitherof the new packet or a retransmission packet. For the sake ofconvenience, the former case is called method 1 and the latter is method2.

In step 630, the UE determines if the timer T(active_period_end) hasexpired, that is, whether no packet has been received during the timeT(active_period_end). If the timer T(active_period_end) has expired, theUE goes to step 640. If the timer T(active_period_end) is still running,the UE repeats steps 625 and 627.

In step 640, the UE operates in a different manner depending on method 1or method 2.

In method 1, the UE completes processing of HARQ packets stored in theHARQ processor, upon time-out in step 640 and enters into the sleep modeuntil the next active period starts. The next active period starts whenthe timer T(DRX_CYCLE_LENGTH) expires.

In method 2, the UE enters into the sleep mode without waiting for thecompletion of processing of the HARQ packets because the end of theactive period interval is set with regard to reception of any downlinkpacket irrespective of a new packet or a retransmission packet. If NodeB does not retransmit a particular packet within the end of the activeperiod interval, the UE switches to the sleep mode. Therefore, the NodeB and the UE should send and receive the retransmission version of thepacket during the active period end interval.

In other words, if a retransmission packet does not arrive at the UEwithin the end of the active period interval, this implies that the NodeB has given up transmission of the packet and thus it is impossible forthe UE to receive the packet successfully. Hence, the UE deletes packetsstored in the HARQ processor of which the retransmission versions havenot been received and immediately enters the sleep mode.

Referring to FIG. 7, a UE receiver 700 includes a Demultiplexer (DEMUX)705, an HARQ processor 715, a control channel processor 720, a DRXcontroller 725, and a receiver 730.

Receiver 730 is turned on or off under the control of DRX controller725. DRX controller 725 turns off the receiver in the sleep mode andturns it on in an active period. HARQ processor 715 processes an HARQpacket received from receiver 730 according to a predetermined HARQoperation, and provides an error-free HARQ packet to DEMUX 705.

DEMUX 705 checks the Last Packet Flag of the received HARQ packet. Ifthe Last Packet Flag is set to YES, DEMUX 705 reports it to DRXcontroller 725 and also provides the received packet to a higher layer.

Upon sensing the reception of the packet with the Lat Packet Flag set toYES, DRX controller 725 monitors the status of HARQ processor 715. Whenprocessing of HARQ processor 715 is completed, DRX controller 725 entersthe sleep mode, that is, turns off receiver 730.

Control channel processor 720 processes information received on adownlink shared control channel. If the end of the active period issignaled by the downlink shared control channel as with the secondexemplary embodiment of the present invention described with referenceto FIG. 5, control channel processor 720 reports the end of the activeperiod to DRX controller 725.

Then, DRX controller 725 monitors the status of HARQ processor 715. Whenprocessing of HARQ processor 715 is completed, DRX controller 725 entersthe sleep mode, that is, turns off receiver 730.

When UE receiver 700 receives the last packet as in the first exemplaryembodiment of the present invention, preferably but not necessarily, itenters into the sleep mode after sending an RLC-level ACK signal (an RLCACK signal, for short) rather than immediately entering into the sleepmode.

This is because in a packet service, the UE operates in an RLCAcknowledge Mode (RLC AM) using an Automatic Repeat reQuest (ARQ)different from the HARQ in order to increase the reliability oftransmission/reception.

In an ARQ operation, a transmitter inserts a serial number into a packetprior to transmission and a receiver determines if there is any failedpacket by checking the serial number. For the failed packet, thereceiver requests a retransmission of the failed packet by sending aNegative ACK (NACK) signal to the transmitter. For a successfullyreceived packet, the receiver sends an ACK signal to the transmitter.The ACK signal and the NACK signal are carried in a control messagecalled an RLC status report.

If a service requiring DRX is provided in the RLC AM, upon receipt ofthe last packet, the UE must send an RCL ACK signal for the last packet.Therefore, the UE preferably enters into the sleep mode after sendingthe RLC ACK signal rather than immediately entering into the sleep mode.

Thus, a description will be made of a method for, upon receipt of apacket piggybacked with a last packet indicator, entering into the sleepmode after sending an RLC ACK signal for the last packet, compared tothe first exemplary embodiment of the present invention.

The UE operates in an active period with no packets to receive in thesame manner as in the first exemplary embodiment of the presentinvention and thus a description of the UE operation in the activeperiod with no packets to receive is not provided herein.

Referring to FIG. 8, the Node B signals a DRX cycle length 810,information for deriving the start position 805 of an active period 850,and a minimum active period length 840 a or 840 b.

The UE wakes up at each of the starting positions 805, 820 and 825 ofactive periods 850, 860 and 870. In the absence of data to receive, theUE is kept for the minimum active period length and enters into thesleep mode. In the presence of data to receive, the UE maintains theactive period until receiving the data completely and then enters intothe sleep mode.

The UE calculates the starting position 805 of the active period 850according to a predetermined method, for example, by modulo operation ofan ID of the UE and the DRX cycle length. When the active period startsat the time point 305, the UE is activated.

The lengths of the active periods 850, 860 and 870 variably range fromthe minimum length 840 a or 840 b to the DRX cycle length 810 or 880. Atthe starting position 805 of the active period 850, the UE receives apacket on a downlink channel. Reference numerals 840 a and 840 b denotea physically identical minimum active period length.

As to the active period 860, packets are successively received for theminimum active period length 840 a. The UE can terminate the activeperiod 860 by determining whether each received packet is the last one.

For example, the UE wakes up at the start position of an active periodand monitors a downlink control channel. That is, the downlink controlchannel and downlink packets are sent to the UE before the minimumactive period length 840 a ends. The UE receives the downlink packetsuntil receiving a packet 880 piggybacked with a last packet indicator.The last packet indicator can take the form of an RLC control signal.

The UE operates differently in an active period with packets to receivein the first and fourth exemplary embodiments of the present invention,as follows.

When the UE completely receives a packet piggybacked with a Last PacketFlag set to YES, it terminates the active period and transitions to thesleep mode in the first exemplary embodiment of the present invention.

In the fourth exemplary embodiment of the present invention, when the UEreceives a packet piggybacked with a last packet indicator and completessuccessful reception of all packets with lower serial numbers than thatof the last packet, it sends ACK signals for the packets with the lowerserial numbers, ends the active period, and then enters into the sleepmode.

Let the serial numbers of the packets be denoted by x to x+n, an RLCentity 945 configured for each application in the UE determines if anyRLC PDU has not been received by checking the serial numbers of receivedRLC Packet Data Units (PDUs). Upon receipt of a packet with a lastpacket indicator, the UE sends an RLS status report 885 with receptionstatus information about the RLC PDUs on an uplink channel.

If all the RLC PDUs, RLC PDU [x] to RLC PDU [x+n] have been received,the RLC status report 885 carries ACK signals for the RLC PDUs. Aftersending the RLS status report 885, the UE terminates the active period.

On the other hand, if RLC PDU [x+m] from among RLC PDU [x] to RLC PDU[x+n] has not been received, the UE includes a NACK signal for thefailed RLC PDU in the RLC status report 885. Then the UE maintains theactive period until the failed RLC PDU is completely retransmitted fromNode B.

Referring to FIG. 9, the UE receives information about a DRX cyclelength, starting position deriving information, and a minimum activeperiod length during a call setup in step 905. Then the UE prepares fora DRX operation.

In step 910, the UE derives the starting position of an active periodfrom the starting position deriving information, for example, the ID ofthe UE and the DRX cycle length and determines if the starting positionof the active period has come.

If the active period has not started yet, the UE is kept in a sleepperiod until the starting position of the active period in step 935. Thenext active period starts the DRX cycle length after the startingposition of the active period.

When the active period starts, the UE activates a timerT(DRX_CYCLE_LENGTH) and another timer T(MINIMUM_ACTIVE) in step 915. Thetimer T(DRX_CYCLE_LENGTH) is a timer set to the DRX cycle lengthT(DRX_CYCLE_LENGTH) and the timer T(MINIMUM_ACTIVE) is a timer set tothe minimum active period length T(MINIMUM_ACTIVE).

In step 920, the UE monitors a shared control channel to determine ifthere is a packet to receive. If no packets to receive exist until thetimer T(MINIMUM_ACTIVE) expires, the UE is placed in the sleep modeuntil the next active period starts in step 935. The next active periodstarts when the timer T(DRX_CYCLE_LENGTH) expires.

Conversely, if there is any packet to receive before the timerT(MINIMUM_ACTIVE) expires in step 920, the UE receives the packetaccording to an HARQ operation in step 925.

If the packet is successfully received, the UE determines if thereceived packet is the last one by, for example, checking controlinformation piggybacked in the packet in step 1030. When sending thelast RLC PDU, the RLC transmitter includes control informationindicating the last RLC PDU in the RLC PDU. Thus, the UE determines thepresence or absence of the control information indicating the last RLCPDU in the received RLC PDU in step 1030.

If the received packet is not the last one, the UE continues the packetreception until receiving a packet with control information indicatingthe last packet in step 925.

If the received packet is the last one, the UE constructs an RLC statusreport representing the reception statuses of RLC PDUs received so farin step 940. The RLC status report contains the RLC serial numbers offailed packets and the RLC serial numbers of received packets. As statedbefore, the former RLC serial numbers are called NACKs and the latterRLC serial numbers are called ACKs. Hence, the RLC status reportincludes the NACKs and the ACKs. The NACKs are a set of the serialnumbers of the failed packets and the ACKs are a set of the serialnumbers of the received packets.

In the absence of any NACK in the RLC status report, the UE checks ifthe RLC status report includes an ACK for the last RLC PDU and ACKs forall other RLC PDUs with lower serial numbers that of the last RLC PDU instep 945. If the check result is YES, the UE goes to step 950. If thecheck result is NO, which implies that there is a packet requiringretransmission, the UE goes to step 955.

The UE sends the RLC status report in step 950 and enters into the sleepmode until the next active period starts in step 935. The next activeperiod starts when the timer T(DRX_CYCLE_LENGTH) expires.

In step 955, the UE sends the RLC status report and waits untilretransmissions of RLC packets requiring retransmission in the RLCstatus report are completed. Then, the UE sends an RLC status reportwith ACKs for all RLC PDUs with the lower serial numbers than that ofthe last RLC PDU. The UE enters into the sleep mode until the nextactive period starts in step 935.

Referring to FIG. 10, the UE receiver may have a plurality of RLCentities 1035, 1040, and 1045 configured for respective applications.Some of them may be configured to operate in a DRX mode. For example,RLC entity 1045 operates in the DRX mode.

When the following conditions are all satisfied, RLC entity 1045requests a DRX controller 1025 to terminate the active period.

Condition 1: an RLC PDU piggybacked with a last packet indicator isreceived.

Condition 2: all packets received during the active period aresuccessfully received.

Condition 3: an RLC status report with ACKs for all packets receivedduring the active period is completely sent.

Also, RLC entity 1045 determines if there is any failed packet bychecking the serial numbers of the RLC PDUs and constructs the RLCstatus report according to the determination result.

Upon receipt of a signal indicating the end of the active period fromRLC entity 1045 operating in the DRX mode, DRX controller 1025terminates the active period and maintains the sleep mode until the nextactive period starts.

A DEMultiplexer/Multiplexer (DEMUX/MUX) 1005 multiplexes RLC PDUsreceived from the RLC layer, i.e. RLC entities 1035, 1040 and 1045 intoa MAC PDU, or demultiplexes a MAC PDU received from an HARQ processor1015 into RLC PDUS prior to transmission to RLC entities 1035, 1040 and1045.

HARQ processor 1015 processes an HARQ packet received from a transceiver1030 according to a predetermined HARQ operation and provides anerror-free HARQ packet to DEMUX/MUX 1005. DEMUX of DEMUX/MUX 1005provides the received HARQ packet to RLC layer 1035, 1040, and 1045.

Also, HARQ processor 1015 provides a MAC PDU received form the DEMUX ofthe DEMUX/MUX 1005 to the transceiver according to the HARQ operationand the transceiver 1030 sends the MAC PDU to the Node B.

A control channel processor 1020 processes information received form adownlink shared control channel. If the information indicates thepresence of a packet destined for the UE, control channel processor 1020reports the presence of a packet to receive to DRX controller 1025.

DRX controller 1025 finds out the start position of an active period andturns on a receiver at the start position. If DRX controller 1025 doesnot receive the report indicating the presence of a packet to receivefrom control channel processor 1020 until a minimum active period lengthexpires, it terminates the active period.

On the other hand, upon receipt of the report indicating the presence ofa packet to receive, DRX controller 1025 maintains the active perioduntil it receives a signal indicating the end of the active period fromRLC entity 1045.

As is apparent from the above description, the present inventionincreases a UE waiting time by defining a DRX operation for a connectedUE considering service characteristics in a future-generation mobilecommunication system. Therefore, the power consumption of the UE isminimized.

For a packet service in which traffic generation status may vary everyDRX cycle, adjusting an active period length according to therequirements of traffic at a reception time provides a DRX operation.

Also, the UE enters into a sleep mode after confirming successfulreception of packets including retransmission packets and sending an RLCACK signal for the packets. Therefore, the reception performance of thepackets is increased.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the presentinvention as further defined by the appended claims and theirequivalents.

What is claimed is:
 1. A method for wireless communication, the methodcomprising: transitioning to an active state from a sleep state;extending an active time of the active state, if control data indicatinga transmission of new user data is received on a control channel;receiving a control signal indicating a termination of the active time;and transitioning to the sleep state from the active state, based on thecontrol signal.
 2. The method of claim 1, further comprising monitoringthe control channel during the active time.
 3. The method of claim 1,wherein the termination of the active time comprises stopping at leastone of a first timer and a second timer.
 4. The method of claim 3,further comprising: stopping at least one of the first timer and thesecond timer, if the control signal indicates that the at least one ofthe first timer and the second timer is to be terminated.
 5. The methodof claim 1, wherein extending the active time of the active statecomprises: starting a first timer to monitor for the control data on thecontrol channel, the control data being associated with user data to betransmitted; and starting a second timer, if the control data indicatingthe transmission of the new user data is received on the control channelwhile the first timer is running.
 6. The method of claim 1, whereinextending the active time of the active state comprises: starting afirst timer to monitor for the control data on the control channel, thecontrol data being associated with user data to be transmitted; andrestarting a second timer, if the control data indicating thetransmission of the new user data is received on the control channelwhile the second timer is running.
 7. The method of claim 1, wherein thecontrol channel includes a physical downlink control channel (PDCCH). 8.An apparatus for wireless communication, the apparatus comprising: areceiver; and a controller configured to transition the apparatus to anactive state from a sleep state, extend an active time of the activestate, if control data indicating a transmission of new user data isreceived on a control channel through the receiver, receive, through thereceiver, a control signal indicating a termination of the active time,and transition the apparatus to the sleep state from the active state,based on the control signal.
 9. The apparatus of claim 8, wherein thecontroller further is configured to monitor the control channel duringthe active time.
 10. The apparatus of claim 8, wherein the terminationof the active time comprises stopping at least one of a first timer anda second timer.
 11. The apparatus of claim 10, wherein the controller isfurther configured to terminate at least one of the first timer and thesecond timer, if the control signal indicates that the at least one ofthe first timer and the second timer is to be terminated.
 12. Theapparatus of claim 8, wherein the controller is further configured tostart a first timer to monitor for the control data on the controlchannel, the control data being associated with user data to betransmitted, and start a second timer, if the control data indicatingthe transmission of the new user data is received on the control channelwhile the first timer is running.
 13. The apparatus of claim 8, whereinthe controller is further configured to start a first timer to monitorfor the control data on the control channel, the control data beingassociated with user data to be transmitted, and restart a second timer,if the control data indicating the transmission of the new user data isreceived on the control channel while the second timer is running. 14.The apparatus of claim 8, wherein the control channel comprises aphysical downlink control channel (PDCCH).
 15. A method for wirelesscommunication, the method comprising: transmitting, by a Node B,information for deriving a starting position of an active state to auser equipment (UE); transmitting, by the Node B, to the UE, controldata on a control channel, the control data indicating a transmission ofnew user data; and transmitting, by the Node B, a control signalindicating a termination of an active time, wherein the active time ofthe active state is extended, if the control data indicating thetransmission of the new user data is transmitted.
 16. The method ofclaim 15, wherein further comprising transmitting data packets to the UEduring the active time.
 17. The method of claim 15, wherein thetermination of the active time comprises stopping at least one of afirst timer and a second timer.
 18. The method of claim 17, wherein theUE stops at least one of the first timer and the second timer, if thecontrol signal indicates that the at least one of the first timer andthe second timer is to be terminated.
 19. The method of claim 15,wherein the UE starts a first timer to monitor for the control data onthe control channel, the control data being associated with user data tobe transmitted, and starts a second timer, if the control dataindicating the transmission of the new user data is received on thecontrol channel while the first timer is running.
 20. The method ofclaim 15, wherein the UE starts a first timer to monitor for the controldata on the control channel, the control data being associated with userdata to be transmitted, and restarts a second timer, if the control dataindicating the transmission of the new user data is received on thecontrol channel while the second timer is running.
 21. The method ofclaim 15, wherein the control channel includes a physical downlinkcontrol channel (PDCCH).
 22. An apparatus for wireless communication,the apparatus comprising: a transmitter; and a controller configured totransmit, to a user equipment (UE), through the transmitter, informationfor deriving a starting position of an active state, transmit, to theUE, through the transmitter, control data on a control channel, thecontrol data indicating a transmission of new user data, and transmit,through the transmitter, a control signal indicating a termination of anactive time, wherein the active time of the active state is extended, ifthe control data indicating the transmission of the new user data istransmitted.
 23. The apparatus of claim 22, wherein the controllerfurther is configured to transmit data packets to the UE during theactive time.
 24. The apparatus of claim 22, wherein the termination ofthe active time comprises stopping at least one of a first timer and asecond timer.
 25. The apparatus of apparatus 24, wherein the UE stops atleast one of the first timer and the second timer, if the control signalindicates that the at least one of the first timer and the second timeris to be terminated.
 26. The apparatus of claim 22, wherein the UEstarts a first timer to monitor for the control data on the controlchannel, the control data being associated with user data to betransmitted, and starts a second timer, if the control data indicatingthe transmission of the new user data is received on the control channelwhile the first timer is running.
 27. The apparatus of claim 22, whereinthe UE starts a first timer to monitor for the control data on thecontrol channel, the control data being associated with user data to betransmitted, and restarts a second timer, if the control data indicatingthe transmission of the new user data is received on the control channelwhile the second timer is running.
 28. The apparatus of apparatus 22,wherein the control channel comprises a physical downlink controlchannel (PDCCH).